Railroad signal systems are used to relay electrical power and signals from a central location, such as a wayside shed, over long distances to track switches, rail crossings, signal lights and other devices used in rail control. Power is distributed to these remote control devices from the central location through individual circuits arranged in an array at the central location and terminated via threaded posts, typically using ring terminated wires secured to the posts using nuts. Surge protection is typically provided for each circuit in the system, with a surge protector terminated to the threaded posts and bridged to a ground bus. FIG. 1 is an illustration of a prior art terminal block in which a wire coming into the system from the field is attached to a threaded post with a ring terminal. The field wire is secured to the post with a nut. The field wire is in electrical communication with a “house” wire that is typically locally connected elsewhere within the rail logic control system at the central location via a second threaded post. The field and house wires are also in electrical communication with a spark gap surge protection device contained within a transparent housing via the threaded posts and which is connected to ground via a third threaded post in the event of an overvoltage condition.
This arrangement, an example of which is shown in FIG. 1, is a mature technology that has generally worked well over time in its operation. However, servicing these systems is labor intensive and has numerous drawbacks associated with maintaining them.
For example, the AREMA manual recommends a periodic test of each field wire to verify its insulation integrity, sometimes referred to as a “megger” test. In the case of most rail control systems, each of what may be many hundreds of individual wires must be independently separated from the circuit for testing with a 1000 VDC charge, then reconnected before the next wire can be tested. For switching of circuits, a system of nuts and leaf springs are used that disconnects the circuit by removing the nut, sometimes referred to as the “golden nut.” As a result, conducting an insulation integrity test with current technology requires loosening and removing each nut, testing, and the reattachment/retorquing of the nut, which can easily be dropped or become lost, increasing time and expense. Additionally, the leaf spring used in combination with the nut is not always as reliable as might be desired if the proper torque is not applied to the nuts, which have to be checked periodically to avoid circuits coming loose as a result.
The advent of new rail safety protocols, including increased frequency of inspection and testing procedures, combined with other advancements in technologies that can increase the number of safety and control devices implemented along a given section of rail is likely to amplify the drawbacks associated with servicing current rail logic control systems. These drawbacks may be compounded by the need to use larger, more complicated distribution arrays that take up a significant amount of space at the central location, which is often little more than a small shed or cabinet.
Among other disadvantages faced in current rail logic system arrays include that the existing system takes a long time to terminate. Field wires in railroad signal systems are typically a 6 AWG or other heavy gauge wire; these wires must typically be stripped and bent and attached to ring terminals, all of which takes a significant amount of effort because of the thickness of the wire. Furthermore, in current equipment practice it is not always clear when the circuit is disconnected; as a result, because the threaded studs are exposed and not safe to touch when energized, safety issues may be present also.
As previously mentioned, circuit termination arrangements in current rail control systems further include surge protection to protect against overvoltage situations which may occur, for example, during lightening strikes that follow the field wires back to the point where a particular device connects to the array in the control system at the central location. The surge protector used in conventional systems, sometimes referred to as an “ice cube” because of its transparency and shape, is bolted down and can take a long time to maintain. Furthermore, the surge protection does not have a readily identifiable good/bad indication for monitoring alarms remotely, and in some cases even on-site visual inspection can be difficult despite the transparent walls, which may become dirty or cloudy from past surge events.
These and other drawbacks are present in current railroad signal systems.